1. Field of the Invention
The present invention relates to an image forming apparatus which heats and fixes a toner image onto a sheet, and particularly to a technique to prevent a paper jam in a fixing unit.
2. Description of the Related Art
Hitherto, when a sheet (so-called back side of paper) in which an image has already been printed on the back surface of the sheet opposite to the front surface on which an image is to be formed is used, there is a case where the back surface of the sheet is adhered to a pressure roller by the influence of the toner of the image printed on the back surface of the sheet and is wound therearound. There is disclosed a technique in which in order to prevent this, the image density of the back surface of a sheet is detected, and a peeling pawl is used according to the detection result to prevent the winding of the sheet around the pressure roller (JP-A-2004-252377).
However, in the related art, since the opportunity of contact between the pressure roller and the peeling pawl is increased, there can occur a problem that the pressure roller is damaged, the toner or paper powder adheres to the peeling pawl and the image is distorted, or the peeling performance is reduced by the abrasion of the peeling pawl. Besides, since a complicated mechanism is required in order to cause the peeling pawl to come in contact with or to be separated from the pressure roller, a reduction in cost of the apparatus is hindered.